Concrete structures such as columns in salt water tend to corrode at the location above the salt water in the inter-tidal zone where the column is subject to wetting and drying and in the splash zone and above where the concrete is occasionally exposed to salt water.
One solution to this problem is to surround the column with a jacket containing a layer of grout within which is buried or located a sacrificial anode as a mesh or layer surrounding the column. This anode is electrically connected to the steel in the column to set up an electric current through the connection and an ionic current through the electrolyte and the concrete from the anode to the steel to tend to inhibit the corrosion of steel in favour of the corrosion of the sacrificial anode.
A recent example of an arrangement of this type is shown in U.S. Pat. No. 7,520,974 issued Apr. 21, 2009 by the present Applicant. Further examples are shown in prior U.S. Pat. No. 5,714,045 (Lasa) assigned to Alltrista Corporation and issued Feb. 3, 1998 and in U.S. Pat. No. 4,692,066 (Clear) issued Sep. 8, 1987.
The present Applicant in U.S. Pat. No. 7,520,974 issued Apr. 21, 2009 discloses a modified arrangement in which an impervious sealed sleeve is provided which carries no anode itself but which cooperates with an anode body in the water below the sleeve. The sleeve acts to inhibit permeation of oxygen through the concrete to the steel and at the same time acts to promote transfer of current from the anode through the concrete under the sleeve by preventing drying by preventing moisture escape. An anode arrangement may be provided only at the top of the sleeve to consume oxygen in that area. The sleeve may be applied over a layer of grout. The top edge surface of the grout may be sealed from the sleeve to the column.
The disclosures of each of the above documents are incorporated herein by reference.
It is also known to simply clamp an anode onto the column below water level to protect the portion of the column within the water. As the salt water is highly conductive, most of the current generated is transferred to steel in the wet portion of the column and little of the current generated in the galvanic action is transferred to the area of most corrosion which is the area at and above the water line which is wetted and dried. This problem is discussed in the above patent of Clear.
In some cases, as shown for example in Lasa above, the above jacket and anode arrangement is used with a below water additional anode, commonly known as a bulk anode, so as to avoid the lower part of the mesh anode in the jacket which is mostly or wholly below water from being rapidly corroded and lost.
In other cases, for a simple inexpensive repair with no cathodic protection, a simple wrapping is applied around the column at the water line so as to cover up and hide the worst of the damage. This arrangement may provide a physical barrier but of course does not provide any cathodic protection by galvanic action so that the underlying corrosion continues. As discussed in Lasa above, this type of repair is considered to be merely cosmetic, merely acting to cover up the worst of the cracking and exposed steel. However this can provide a cheap fix with short life span of protection. The wrapping can surround a layer of grout which covers the worst of the cracking and repairs any holes or the wrapping can be applied directly to the column. In some cases the wrapping is filled with a non-cementitious material such as epoxy.